Process for the modification of the mechanical characteristics of carbon steel wire

ABSTRACT

THE INVENTION DEALS WITH A PROCESS FOR THE MODIFICATION OF THE MECHANICAL CHARACTERISTICS OF CARBON STEEL WIRE, CONSISTING OF THE FOLLOWING FIRST PATENTING, THEN COLD DEFORMING, AND FINALLY DEFORMING SAID WIRE AT A TEMPERATUR ABOVE THE AMBIENT TEMPERATURE BUT BELOW THE RECRYSTALLIZATION TEMPERATURE OF THE STEEL IN SAID WIRE, BY APPLYING TRANSVERSE FORCE TO SAID WIRE.

I. BEHAR May 25, 1971 PROCESS FOR THE MODIFICATION OF THE MECHANICALCHARACTERISTICS OF CARBON STEEL WIRE Filed Sept. 29. 1967 SSheets-Sheetl May 25, 1971 BEHAR 3,580,746

, PROCESS FOR THE MODIFICATION OF THE MECHANICAL HARACTERISTICS OFCARBON STEEL WIRE Filed Sept. 29, 19 3 Sheets-Sheet 8 E'Sii Fig 4;;

FIG; 2 13 May 25, 1971 l. BEHAR PROCESS FOR THE MODIFICATION OF THEMECHANICAL CHARACTERISTICS OF CARBON STEEL WIRE 3 Sheets-Sheet 3 FiledSept. 29. 1967 United States Patent 3,580,746 PROCESS FOR THEMODIFICATION OF THE MECHANICAL CHARACTERISTICS OF CARBON STEEL WIREIsaac Behar, Bourg-en-Bresse, France, assiguor to Trefileries &Cableries de Bourg et du Havre, Bourg-en- Bresse, Ain, France FiledSept. 29, 1967, Ser. No. 671,720 Claims priority, application France,Oct. 4, 1966, 78,740, 78,741 Int. Cl. C21d 9/52 US. Cl. 148-42 8 ClaimsABSTRACT OF THE DISCLOSURE The invention deals with a process for themodification of the mechanical characteristics of carbon steel wire,consisting of the following first patenting, then cold deforming, andfinally deforming said wire at a temperature above the ambienttemperature but below the recrystallization temperature of the steel insaid wire, by appl ing transverse force to said wire.

Carbon steel wire of high mechanical properties are usually used for themanufacture of springs and the reinforcing of prestressed concrete.

The most frequent compositions used for these purposes are as follows:

Carbon 0.60-0.90 Manganese 0.50-1.25 Silicon 0.10-0.40

The remainder is composed of iron and impurities usually present inindustrial products.

Improved mechanical properties are usually obtained by a succession ofthe following operations:

Patenting by heating to 850950 and rapid cooling to 400-550";

Cold drawing (the wire being drawn through several draw-plates (dies)which progressively reduce the section of the wire).

The patented and cold drawn wires are wound around a capstan and arethus presented in the form of a coil.

For the application of these wires to prestressed concrete and certainsprings the following properties should be obtained:

(a) a sufficient degree of straightness, (b) a high tensile strength,

(0) a high elastic limit,

(d) a high elongation value.

Existing drawn wires do not adapt themselves to these applications,because although they have a high tensile strength their elastic limitand elongation factor are too low, and they also present a curvaturecorresponding to the form of the wire drawing rollers.

The wires must therefore undergo a straightening treatment and theelastic limit and elongation factor must be increased.

There exist means of mechanical straightening which consist ofsubjecting the wire to alternate and gradually decreasing stresses.

The practical methods generally used are as follows:

(a) The wire is passed through two rollers placed at 90 to each other,and is successively subjected to gradually decreasing angulardeflections.

(b) The wire is passed through eccentric dies which form part of arotating framework. The wire is thus simultaneously subjected toalternate bending forces on each of its generatrices, as well as toalternate torsional forces, increasing progressively and then decreasingin the direction of movement of the wire.

The straightening resulting from these two known methods produces astraight wire with an improved elongation factor, but the disadvantagesare that the tensile strength, and above all the elastic limit, which isalready low after drawing, are decreased.

The mechanical properties may also be modified by cold rolling atambient temperature and by hot rolling at a temperature high enough forthe recrystallization of the steel during the process. The hot rollingis usually carried out at the AC3 point of steel, i.e. above thetemperature at which the steel passes from the body centred cubicstructure to a face centred cubic structure.

At ambient temperature, the steel possesses a low plasticity and forcold working numerous reducing stages are necessary; it is evennecessary occasionally to interrupt the cold treatment in order to carryout a recrystallization process (heat treatment).

The hot rolling, being carried out at recrystallization temperature,allows much greater deformation than at ambient temperature, but resultsin a lower mechanical resistance.

The main purpose of the invention is to remedy these inconveniences. Itdeals with, in effect, a process for the modification of the mechanicalproperties of carbon steel wire, by means of mechanical straightening,modification of the section or the shape at a temperature above ambientand below the recrystallization temperature of steel. The wire is thencooled to the ambient temperature and wound on to a bobbin of sufiicientdiameter to avoid bending.

Other purposes and advantages of the invention are borne out by thefollowing description and claims and the enclosed sketches of which:

FIG. 1 is a schematic view of an installation to carry out the processof straightening of carbon steel wire;

FIG. 2 is a schematic view of an installation to carry out the processof drawing carbon steel wire;

FIGS. 3, 3a, 3b, 3c, and 3d are views showing the wire sections obtainedby one single rolling operation;

FIGS. 4, 4a, 4b, and 4c are views showing a strand or a group ofparallel wires which are transformed by deformation of the group ofwires.

FIG. 5 is a schematic view showing an alternative method of carrying outthe process;

FIG. 6 is a schematic view showing the manufacture of a wire having ahigh plasticity;

The installation to carry out the process of rectification of carbonsteel wires (FIG. 1) comprises, for eX- ample, a set of rollers-guide 2,through which is passed the wire to be straightened 1; the wire is ledinto a heating zone made up of, for example, an induction heating coil3.

The wire which is at the desired temperature is straightened,mechanically by alternate bending, which is obtained by 2 sets ofrollers 4 and 5 which are placed at at each other; the wire passesthrough a cooler 6 and is then wound around a spool or bobbin ofsufficient diameter to avoid bending.

The tables of comparison 1 and 2 indicate the advantages offered by theinvention as compared to the normal processes.

TAB LE 1 Straightening at- Ambient temperature plus annealing at 280 0.280 C.

yield point, percent In both cases the wire used had the followingcomposition:

Percent Carbon 0.80 Manganese 0.70 Silicon 0.20 Sulphur and phosphorus0.06

The remainder: iron and impurities.

After patenting and cold drawing from 11 mm. to 7 mm. the followingproperties were obtained:

Kg./mm. Yield point 173 0.1% yield strength 112 Elongation at yieldpoint for a length of 500 mm.:

Following the usual procedure the wire is straightened at ambienttemperature by alternate bending, then treated at 280 C., cooled andwound.

The properties obtained after straightening and annealing are noted inTable 1; after straightening at ambient temperature, the wire has thefollowing properties:

Yield point 172 0.1% yield strength 108 Elongation at yield point for alength of 500 mm.:

In accordance with the process described in the invention, the wire isheated to 280 C. and straightened by alternate bending at this sametemperature, then cooled and wound at ambient temperature, as shown onthe accompanying drawing.

It may be noticed in the quoted example that the straightening atambient temperature decreases the yield point and yield strength whichare afterwards restored by the final annealing; the yield point aftermechanical straightening at ambient temperature and annealing at 280 C.therefore closely resembles the yield point of the wire after drawing.

By contrast, in the process described by the invention the straighteningat the annealing temperature not only prevents the reduction of theyield point of the wire, but actually increases it; also, the elasticlimit of the wire is higher, which is a valuable property when the wireis used in springs and reinforcements of pro-stressed concrete.

The wires produced following the process of this invention also possessimproved properties of creepage and stress relief.

When a spring is maintained under constant load it has a tendency toextend through the eifect of creepage and the spring is considered moresatisfactory when the extension produced by a constant effort is held toa minimum.

However, in the case of pre-stressed concrete reinforcements which aremaintained at a constant length or in the case of springs which aresubject to constant deformation it is established that the initialtension of the reinforcements or of the spring diminish progressivelywith time under the eifect of stress relief.

The steels which are used for the compression of cement or in the formof springs are considered much better 4 whendthe stress relieving takesplace during a shorter peno Table 2, which contains the values ofcreepage and of stress relief for a steel straightened at ambienttemperature and annealed following a conventional process, and for thesame steel straightened following the new process which is the subjectof this invention, at a temperature, above ambient and less than thetemperature of recrystallization, shows the important differences inresulting properties.

It is noted that the process of the invention reduces the stressrelieving and the creepage in considerable proportions thus allowing asubstantial economy of steel.

The process applied carbon steel wires consists, as is represented byFIG. 2, in straightening the wire 1 by leading it through the sets ofrollers placed at to each other 8 and 9 and/or passing it through theguides.

Having completed the straightening, the wire is heated, for example, bymeans of an induction heating coil 4 which brings the wire temperatureto about 300 C.

The wire is then compressed in one single passage at this temperaturebetween a set of rollers 11.

The flat wire thus obtained (FIG. 3b) is cooled to ambient temperatureduring its passage through the cooler 12 and is then wound on to aspecial spool or reel 7.

The above process was applied using principally a wire of 8 mm. having acarbon content of 0.60%, manganese of 0.65%, sulphur and phosphorus of0.06%. The remainder was comprised of iron and the impurities usuallyfound in commercial steels. This wire was patented (to 900 C. and rapidcooling to 500 C.) then descaled, dephosphated and drawn on aconventional drawing machine in several passes from 8 mm. to 5 mm.

The wire which was treated following the above process had the followingcharacteristics:

Cold drawing Drawing followed by and cold 300 C.

rolling, rolling,

percent percent Elongation of 500 mm. length 5. 8 Creep loss after 2hours tension at 80% yield point 0. 05 0. 008 Percent relaxation lossafter tension for 120 hours at 70% of the yield point 5. 3 1.2

A low creep loss is advantageous for applications where springs aresubjected to a constant load, because as a result of this, the plasticdeformation will be less and consequently the life of the spring will beincreased.

The low relaxation losses in wires produced by this process oiferadvantages in applications where springs are subjected to a constantload as well as the application of wires for concrete under compression(steels for prestressed concrete).

In these two cases the wires under load lose their initial tension lessrapidly than if they were manufactured according to the other describedprocess.

The process is equally applicable when the section required has acomplex form with concave and convex sections. The wire, having beenalready heated to between C. and the crystallization temperature, passesthrough grooved rolling cylinders which contain convex and concavezones, corresponding to the section required on the finished wire.

-In FIGS. 3, 3a, 3b, 3c, and 3d are shown non-limiting examples ofsections obtainable by a single rolling passage. In the productionmethod shown in FIG. 4, a. strand or a group of parallel wires 14,consisting of separate wires is transformed by one pass of the rollerinto triangular (FIG. 4a), round (FIG. 4b), or oval (FIG. 3c) sections.

In the method shown by FIG. 5, the wire is subjected to two passes ofthe roller at a temperature above ambient and below crystallizationtemperature; the wire 1 passes successively through the straighteningrollers or guides 8 and 9 and is then brought up to temperature by meansof a self induction heating coil 10. The wire is subjected to apreliminary transformation by the cylinders 11 and is then wound onto acapstan 13 Following this, it is led into the induction heating zone 10before another transformation process by means of a set of 4 drawingdies 11 Finally it is cooled 12 and wound on to a special spool beforebeing stored.

iIn the process of manufacture shown by FIG. 6, the wire is subject todrawing or deformation of section at a temperature above ambient andbelow that of recrystallization followed by drawing or deformation ofsection at ambient temperature. The wire 1, already having been treated,is brought into the induction heating zone 10 and is subjected todeformation between the rollers 11, at a temperature between 100 C. andthat of recrystallization.

The wire is then cooled by a cooler 12 and is cold drawn by means of adie 15 before being wound onto a spool or bobbin 13.

The type of process is particularly suited to the manufacture of a wirehaving a high modulus of elasticity. The elastic limit of the wire islowered by means of a passage through the drawing dies 15 at ambienttemperature.

Another variant of the process is to obtain the final section by drawingthe wire at a temperature between 100 C. and that of recrystallization.Then the elastic limit is reduced by submitting the wire to alternatebending efforts at ambient temperature, by passing it through astraightener.

The invention, of course, is not limited to the examples of manufacturedescribed above and by the accompanying drawings, but may also embodyother ways and means of manufacture without exceeding the limits of thespecification; for example, the scope of the invention is not exceededif the cylinders of the rolling mills are replaced by any otherarrangement for modifying the form or section of the wire, regardless ofthe section so obtained, providing that the wire is previously heated toa temperature between 100 C. and that of recrystallization and thenundergoes deformation in this temperature zone.

Similarly, it is possible to combine several methods of deforming thewire, each method being carried out while the temperature of the wire isbetween C. and the temperature of recrystallization of steel.

It is equally possible to combine methods of deformation carried outwhile the temperature of the wire is between 100 C. and therecrystallization temperature with deformation produced at ambienttemperature; the latter deformation is carried out between 100 C. andrecrystallization temperature when a higher elastic limit is required,and at ambient temperature for a wire with a high modulus of elasticity.

Finally the induction heating coils may be replaced by any other knowntype of heating such as: The Joule effect, gas burners, molten metalsetc.

What we claim is:

1. Method of making an elongated medium or highcarbon steel producthaving a high ultimate tensile strength, a high elongation at rupture,and a high elastic limit, which method comprises the steps of patentingan elongated hot-rolled product, subjecting said product to coldmechanical deformation, heating said product to a temperature in excessof the ambient temperature and below the temperature ofrecrystallization of the steel therein, and then subjecting said steelproduct at said last mentioned temperature to permanent deformation byapplying force thereto in directions transverse to the longitudinal axisof said elongated product.

2. Method as claimed in claim 1 in which said elongated product is asteel wire.

3. Method as claimed in claim 1 in which said elongated product is abundle of steel wires.

4. Method as claimed in claim 1 in which said cold deformation isproduced by drawing said elongated prodnot.

5. Method as claimed in claim 1 in which said cold deformation isproduced by cold rolling.

6. Method as claimed in claim 1 in which said elongated product isstraightened during said last-mentioned step, by flexing it in oppositedirections.

7. Method as claimed in claim 1 in which said product is permanentlydeformed at said last-mentioned temperature by rolling it.

8. Method as claimed in claim 1 in which said last mentioned step iscarried out at from 100 to 500 C.

References Cited UNITED STATES PATENTS 3,196,052 7/1965 Hann l48122,816,052 12/1957 HOE et al. 148-42 2,767,836 10/ 1956 Nachtman 148-122,589,881 3/1952 Sims et al. 14812 2,281,132 4/1942 Young 148-12 L.'DEWAYNE RUTLEDGB, Primary Examiner W. W. STALLARD, Assistant Examiner

